This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Studies in infants suggest that long chain highly unsaturated fatty acids (LCHUFA, omega-3 fatty acids) are absorbed with less efficiency that other dietary fats. The cumbersome nature of fat balance studies has deterred researchers from confirming that this difference maintains in adults. Moreover, data from a pilot study we recently conducted in the GCRC suggest that genetic variation in the APOA4 gene may modulate the efficiency of LCHUFA absorption. Jandacek et al. have established that sucrose polybehenate, a component of the FDA approved fat substitute Olestra, can serve as an non-absorbable marker in a highly accurate measurement of intestinal dietary fat absorption. We propose a pilot GCRC-based study to examine whether the APO4 T347S polymorphism affects the efficiency with which dietary LCHUFA are absorbed in adults.